This application addresses broad Challenge Area (14) Stem Cells and specific Challenge Topic, 14-DK-101 Induced pluripotent stem cells--cellular and humanized mouse models of disease. The liver is the main site of intermediary metabolism of amino acids, carbohydrates, lipids and xenobiotics. Metabolic pathways, especially those of xenobiotic compounds, are highly species specific and can vary even between individuals of the same species. Furthermore, many of the therapeutic strategies - especially gene therapy - envisioned for the treatment of metabolic disorders would be optimally tested in human hepatocytes. We have developed a highly efficient and robust method for the repopulation of murine liver with human hepatocytes and replacement levels of >90% can be achieved. We also have developed the technique to convert human skin fibroblasts into hepatocytes in vitro. Here, we propose to utilize a combination of these methods to produce murine models of human hepatic metabolism. Specifically, we plan to model common inborn errors of lipid metabolism as well as the most common genetic variants of hepatic drug metabolism. PUBLIC HEALTH RELEVANCE: Here we propose to generate mice harboring humanized livers that can be used to study and treat inborn errors of human liver function. This will be achieved by first generating induced pluripotent stem cells from skin cells isolated from patients with hepatic metabolic disorders. These cells will be differentiated into hepatocytes that will be used to repopulate the livers of FRG mice. We have shown that this mouse allows replacement of 90% of its liver with human hepatocytes. These mice will allow the study of metabolic deficiencies, analyses of drug metabolism, screens for novel pharmaceutical treatments of metabolic diseases, as well as form the basis for testing stem cell based gene therapy.